It seems that legislation and the highway code have been ammended and now actually discriminate against motorhomes.
The authorities have been banging on for years about having to park in official places but now it is a n offence and carries fines.
A summary of the legislation Google Translated is:
1. Without prejudice to the provisions of articles 49 and 50, overnight stays and parking of motorhomes or the like are prohibited outside places expressly authorized for this purpose.
2. For the purposes of the preceding paragraph, it is considered:
a. 'Parking' means the parking of the vehicle with more space than its perimeter;
b. 'Motorhome or similar' means a vehicle that has a living space or that is adapted for the use of a living space, classified as a 'motorhome', 'special bedroom' or c. 'caravan' by the Institute of Mobility and Transport, IP;
c. 'Overnight' means the stay of a motorhome or similar at the parking place, with occupants, between 9:00 pm on one day and 7:00 am on the following day.
3. Anyone who violates the provisions of paragraph 1 shall be sanctioned with a fine of (euro) 60 to (euro) 300, unless it is an overnight stay or parking in areas of the Natura 2000 network and protected areas, in which case the fine is ( euro) 120 to (euro) 600 (euro).
Makes the UK seem motorhome friendly by comparison
Source of the information is https://campingcarportugal.com/forum/viewtopic.php?f=12&t=9210
If it ain't broke..... Don't fix it!